Fusing apparatus

ABSTRACT

A fusing apparatus is provided for heat fusing a toner image to a sheet of final support material. The apparatus includes a source of heat radiation for application to the sheet. A fusing zone is defined wherein the heat source is effective to fuse the image to the sheet and a flow of air is present at the zone. Means are provided cooperating with the fuser for reducing curl of the sheet during fusing. The curl reducing means comprise at least one seal adjacent the fusing zone for limiting air flow at the zone to an amount at which curl of the sheet is substantially reduced.

[ 1 Nov. 26, 1974 Lowes et 219/216 3,207,129 9/1965 Limberger......,..,..............., 3,291,468 12/1966 Albertsen et a1. 3,505,497 4/1970 Primary ExaminerJohn J. Camlby Assistant Examiner-Henry C. Yuen Attorney, Agent, or Firm-Paul Weinstein; Clarance A. Green; James J. Ralabate [57] ABSTRACT A fusing apparatus is provided for heat fusing a toner image to a sheet of final support material. The apparatus includes a source of heat radiation for application to the sheet. A fusing zone is defined wherein the heat source is effective to fuse the image to the sheet and a flow of air is present at the zone. Means are provided cooperating with the fuser for reducing curl of the sheet during fusing. The curl reducing means comprise at least one seal adjacent the fusing zone for limiting air flow at the zone to an amount at which curl of the sheet is substantially reduced.

10 Claims, 3 Drawing Figures Inventors: David P. Bierworth; Frank R.

Hynes, both of Rochester, NY.

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: Dec. 4, 1973 Appl. No; 421,710

11.8. 34/155, 34/242, 432/242 [51] Int. [58] Field of Search................

[56] References Cited UNITED STATES PATENTS 3,040,702 6/1962 Eng et a1. 3,071,866 l/1963 Mangus......... 3,090,134 5/1963 Morrison......,.,....,................

United States Patent Bierworth et a1.

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FUSING APPARATUS BACKGROUND OF THE INVENTION This invention relates to a fusing apparatus for heat fusing a toner image to a sheet of final support material including means for reducing curl of the sheet during fusing.

When a sheet of final support material having a toner image on a side thereof is subjected to fusing by means of a radiant heat fuser some of the moisture in the sheet is driven out. Depending on the quantity of moisture driven out changes in the length and width of the sheet occur as well as a severe curl. Curl in the resulting sheet after fusing is a severe problem for a reproducing machine, particularly those of the xerographic type. The tendency of the sheet to curl during fusing is one of the causes of jams in the region of the fuser. Curl is also a significant problem in reproducing machines adapted to provide images on both sides of the sheet, a process referred to in the art as duplexing. A duplexing apparatus requires that the sheet be refed through the ma chine. Sheets with a severe curl are extremely difficult and sometimes impossible to feed without persistent jamming problems along the paper path.

The problem of sheet curl due to radiant heat fusing has been recognized in the art as exemplified by US. Pat. Nos. 2,807,703 and 2,807,704. In these patents the fusing apparatus is designed to selectively heat the toner image on the sheet to its fusing point while leaving the sheet per se at a temperature sufficiently below the fusing point of the toner or avoid curl. In fact, the temperature of the sheet is maintained below the boiling point of water so that a substantial portion of the original moisture content of the sheet is not removed. The apparatuses described in these patents are particularly applicable to record cards. In the first of these patents, three embodiments of the fusing apparatus for carrying out the invention are described. In each apparatus the transfer of heat energy to the record card by conduction and convection is kept negligible by a suitable means, and thereby, since the record card per se is made from paper stock and does not readily absorb radiant energy, the temperature of the record card is kept at a lower value than the boiling point of water. Transfer of heat energy by conduction and convection is reduced either by heat extraction or so called fixing station cooling, or by the use of a heat transfer barrier for preventing heat transfer by conduction and convection such as a water filled glass jacket, or in accordance with the third embodiment, by focusing and concentrating the radiant energy on the toner image.

While the approaches of these patents may operate satisfactorily for fusing toner images on record cards, this would not necessarily follow for fusing toner images on support sheets of other types. Toner images on record cards are generally not very dense and, therefore, comprise very little toner so that not as much heat energy is required to fuse them. Conventional copying machines can provide denser toner images containing considerably greater proportions of toner over the sheet surface, which would require a greater quantity of heat energy to fuse them to the sheet. Therefore, it is possible that the apparatuses of the aforenoted patents would not operate satisfactority in the environment of a copying machine since by maintaining the temperature of the sheet below the boiling point of water insufficient heat energy would be impressed on the toner image to consistently fuse the toner image to the sheet.

SUMMARY OF THE INVENTION In accordance with this invention a fusing apparatus has been developed wherein curl of the sheet during fusing is substantially reduced or eliminated. The fuser includes a source of heat radiation. A fusing zone is defined wherein the heat source is effective to fuse a toner image to a sheet of final support material. A flow of air is present at the zone due to influences which are internal and/or external of the fuser. In accordance with this invention the curl reducing means comprises at least one seal adjacent to the fusing zone which limits the air flow at the zone to an amount at which curl of the sheet is reduced or eliminated.

Contrary to the aforenoted prior art teachings in accordance with this invention, the air flow has to be limited severely in order to reduce moisture gradients and to prevent the moisture driven off from the sheet from being completely withdrawn from the fusing zone.

In accordance with preferred embodiments. transport means are provided at the exit and/or entrance regions of the fuser to transport the sheet. One or more of these transports may include suction means for holding the sheet to the transport. The seals preferably extend between the transports and the fuser.

Therefore, it is an object of this invention to provide an improved fusing apparatus for heat fusing a toner image to a sheet of final support material.

It is a further object of this invention to provide an apparatus as above including means for reducing the curl of the sheet during fusing.

It is a still further object of this invention to provide an apparatus as above wherein the curl reducing means includes means for reducing the air flow through the fusing zone.

These and other objects will become more apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows schematically an exemplary reproducing machine including the fusing apparatus of this invention.

FIG. 2 is a perspective view of a sheet of final support material after fusing by a prior art radiant fuser.

FIG. 3 is a cross-sectional side view of the fusing apparatus of this invention including the curl reducing means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 in accordance with this invention, a fusing apparatus 1 is provided for heat fusing a toner image to a sheet 2 of final support material. The fusing apparatus 1 includes a fuser 3 having a source of heat radiation 4 for application to the sheet. The fuser 3 defines a fusing zone 5 wherein the heat source 4 is effective to fuse the image to the :sheet 2. A flow of air is present at the zone 5 due to influences which may be internal and/or external of the fuser 3. An essential part of this invention comprises means which cooperate with the fuser 3 for reducing curl of the sheet 2 during fusing. The curl reducing means 6 preferably comprise at least one seal adjacent to the fusing zone 5 which is adapted to limit air flow through the zone to a volume at which curl of the sheet is substantially reduced.

It is believed in accordance with this invention that paper curl in the final support sheet after fusing by means of a radiant fuser is the result of plastic deformation of the paper sheet. The deformation is made up of two components which may be summed algebraically. One component is related to the type of paper and to the bulk paper changesthat occur during fusing. It is possible to think of these as resulting from one or both of the following: I. a locked in asymmetric residual stress distribution which relaxes or yields under a bulk temperature or moisture level excursion. 2. variations in paper properties across the thickness of the sheet, as for example, the coefficient or expansion with mois' ture. This can result in non-uniform elongation of the sheet and curl in the absence of any assymetry or gradients. The other component is believed to relate to the asymmetrical conditions or gradients imposed on the paper by the fuser and adjacent machine components or other external influences. The curl from this component is always in the direction of the source of radiant energy.

The curl is believed to result from stresses imposed on the sheet associated with the gradient in moisture through the thickness of the sheet. This invention is not directed at preventing curl induced by mechanical deformation which may occur in the copier and which can, in fact, result in curl in either direction depending on the direction of deformation. For example, curl induced by a roll fusing apparatus.

The primary source of the stresses is the moisture gradient which causes the top surface of the sheet to shrink more than the bottom surface. The moisture gradient is determined by the temperature gradient, the initial moisture content and the moisture mass transfer effects. In many cases the moisture mass transfer is significant. In configurations where the fuser is near an air moving device such as a suction box of a vacuum transport the air moving device may aggrevate curl by increasing the rate of moisture mass transfer due to increased air flow in the fusing zone. The rate of moisture mass transfer is substantially increased in the top surface of the sheet thus causing a larger moisture gradient which results in higher stresses and greater deformation of the sheet. Other aspects of the mechanism causing curl in the sheets are described in US. Pat. No. 2,807,703.

The aforenoted description of the mechanism for causing curl is not meant to be limitative of the invention and is presented here by way of example. The aforenoted mechanism is believed to be the mechanism involved in accordance with this invention, however, other factors not yet appreciated could be taking part in the mechanism.

Referring now to FIG. 2, a sheet 2 of final support material is shown after fusing by an apparatus not including the curl preventing means 6 in accordance with this invention. The sheet 2 shown therein has a substantial curl 7 of about 1.5 inches at the trailing edge portion 8 thereof. This type of curl 7 in a sheet 2 is formed by an apparatus 10 as will be described in more detail with reference to FIG. 1 when the curl preventing means 6 are not employed. In other apparatuses the curl 7 may be more or less pronounced. There may be curl 7 at the trailing 8 and/or the leading 9 edges of the sheet 2. Irrespectively, by following the teachings of the present invention, it should be possible to substantially reduce or eliminate curl 7 from the sheet 2 due to fusing when the curl is produced by means other than mechanical deformation.

Referring now to FIG. 1, there is shown by way of example an automatic xerographic reproducing machine 10 which incorporates the improved fusing apparatus 1 of the present invention. The reproducing machine 10 depicted in FIG. 1 illustrates the various components utilized therein for producing copies from an original. Although the fusing apparatus 1 of the present invention is particularly well adapted for use in an automatic xerographic reproducing machine 10, it should become evident from the following description that it is equally well suited for use in a wide variety of machines where an image is fused to a sheet of final support material and it is not necessarily limited in its application to the particular embodiment shown herein.

The reproducing machine 10 illustrated in FIG. I employs an image recording drum-like member 11 the outer periphery of which is coated with a suitable photoconductive material 12. One type of suitable photoconductive material is disclosed in US. Pat. No. 2,970,906 issued to Bixby in 1961. The drum 1] is suitably journaled for rotation within a machine frame (not shown) by means of a shaft 13 and rotates in the direction indicated by arrow 13, to bring the image retaining surface thereon past a plurality of xerographic processing stations. Suitable drive means (not shown) are provided to power and coordinate the motion of the various cooperating machine components whereby a faithful reproduction of the original input scene information is recorded upon a sheet 2 of final support material.

The practice of xerography is well known in the art and is the subject of numerous patents and texts including Electrophotography by Schaffert, published in 1965, and Xerography and Related Processes by Dessauer and Clark, published in 1965. The various processing stations for producing a copy of an original are herein represented in FIG. 1 as blocks A to E. Initially, the drum 11 moves photoconductive surface 12 through charging station A. At charging station A an electrostatic charge is placed uniformly over the photoconductive surface 12 of the drum 11 preparatory to imaging. The charging may be provided by a corona generating device of a type described in US. Pat. No. 2,836,725 issued to Vyverberg in 1958.

Thereafter, the drum 11 is rotated to exposure sta tion B where the charged photoconductive surface 12 is exposed to a light image of the original input scene information, whereby the charge is selectively dissipated in the light exposed regions to record the original input scene in the form of a latent electrostatic image. A suitable exposure system may be of the type described in US. Pat. application, Ser. No. 259,181 filed June 2, 1972.

After exposure, drum 11 rotates the electrostatic latent image recorded on the photoconductive surface 12 to development station C wherein a conventional developer mix is applied to the photoconductive surface 12 rendering the latent image visible. A suitable development station is disclosed in US. Pat. application, Ser. No. 199,481 filed Nov. 17, 1971. The application describes a magnetic brush development system utilizing a magnetizable developer mix having carrier granules and a toner colorant. The developer mix is continuously brought through a directional flux field to form a brush thereof. The electrostatic latent image recorded on photoconductive surface 12 is developed by bringing the brush of developer mix into contact therewith.

The developed image on the photoconductive surface 12 is then brought into contact with a sheet 2 of final support material within a transfer station D and the toner image is transferred from the photoconductive surface 12 to the contacting side of the final support sheet 2. The final support material may be paper, plastic, etc., as desired. After the toner image has been transferred to the sheet of final support material 2, the sheet with the image thereon is advanced to a suitable fuser 3, which coalesces the transferred powdered image thereto. One type of suitable fuser is described in 11.8. Pat. No. 2,701,765, issued to Codichini et al in 1955. After the fusing process, the sheet 2 is advanced by snuffing rolls 14 and then by rolls 15 to a catch tray 16 for subsequent removal therefrom by the machine operator.

Although a preponderance of the toner powder is transferred to the final support material 2, invariably some residual toner remains on the photoconductive surface 12 after the transfer of the toner powder image to the final support material 2. The residual toner particles remaining on the photoconductive surface 12 after the transfer operation are removed therefrom as it moves through cleaning station E. Here the residual toner particles are first brought under the influence of a cleaning corona generating device (not shown) adapted to neutralize the electrostatic charge remaining on the toner particles. The neutralized toner parti cles are then mechanically cleaned from the photoconductive surface 12 by conventional means as, for example, the use of a resiliently biased knife blade as set forth in US. Pat. No. 3,660,863 issued to Gerbasi in 1972.

If desired, in accordance with this invention, the sheets 2 of final support material processed in the automatic xerographic reproducing machine can be stored in the machine within a removable paper cassette 17. A suitable paper cassette is set forth in US. Pat. application, Ser. No. 208,183 filed Dec. 15,1971, now US. Pat. No. 3,767,187.

The reproducing apparatus in accordance with this invention can also have the capability of accepting and processing copy sheets 2 of varying lengths. The length of the copy sheet 2, of course, being dictated by the size of the original input scene or information recorded on the photo-conductive surface 12. To this end the paper cassette 17 is preferably provided with an adjustable feature whereby sheets of varying length and width can be conveniently accommodated. In operation the eassette 17 is filled with a stack of final support material 2 of pre-selected size and the cassette is inserted into the machine by sliding along a base plate (not shown) which guides the cassette into operable relationship with a pair of feed rollers 18. When properly positioned in communication with the feed rollers 18, the top sheet of the stack is separated and forwarded from the stack into the transfer station D by means of registration rolls 19.

It is believed that the foregoing description is suff cient for purposes of the present application to illustrate the general operation of the automatic xerographic reproducing machine 1 which can embody the teachings of the present invention.

Referring now to FIG. 3, that portion of the reproducing machine 10 of P16. 1 embodying the fusing apparatus 1 of this invention is shown in greater detail. The view shown is aside view and it should be readily evident that the fusing apparatus extends across the entire sheet in a direction normal to the plane of the Figure. The image bearing sheet 2, after passing through the transfer station D of FIG. 1 upon separation from the photoconductive surface 12, is allowed to fall into Contact with a vacuum belt transport system 20 which conveys the sheet directly to the fusing apparatus 1.

The fusing apparatus 1 shown includes a radiant type fuser- 3. The fuser 3 includes a heated platen 30 mounted to engage the non-image bearing side of the copy sheet 2 which moves in sliding contact therewith as it is transported through the fusing zone. The heated platen 30 is designed so that an eflcient heat flow is established between the platen and the copy sheet 2 to raise the temperature of the sheet rapidly to a level somewhat below the sheets scorch temperature. By controlling the temperature of the: sheet 2 in this man ner the ability of the sheet to act as a heat sink during image fixing is minimized. The radiant energy source for fusing is provided by an infrared quartz lamp 31 which is mounted in a reflector assembly 32 in opposing relationship to the heated platen 30 and in a position to thermally communicate with the newly imaged side of the copy sheet 2. Preferably the spectral output of the lamp 31 is within a range at which the imaging material which may be toner for a xerographic machine 10 is highly absorptive and at which the support material 2 which may be paper is relatively non-absorptive. As a result, the toner images are rapidly raised to the desired fusing temperature while the support sheet 2 remains at a relatively lower temperature. A forced air cooling chamber 33 is provided about the backside of the reflector assembly 32 to cool the fuser 3 in opera tion.

A heating element 34 is provided in the platen 30 to maintain it at the desired temperature during standby periods. When the quartz lamp 31 is operated the preheat element is disconnected and the platen 31) receives its heat input directly from the quartz lamp.

The leading edge of the sheet 2 bearing the image is pushed through the entrance port 35 to the fusing zone 5 and moves in sliding contact over the platen 31) through the fuser exit port 36 into a pair of cooperating transport rolls 41) and 41 which comprise a flame snuffing apparatus. The lower snuffing roll 41 is positioned such that its outer periphery lies below the plane of the fuser platen 30 whereby in operation the snuffmg rolls 40 and 41 are operative to hold the sheet 2 in sliding contact with the fuser platen 30. The sheet is also held in contact with the platen 30 by means of suction communicated via suction chamber 37 and platen suction ports 38.

The snuffing rolls 40 and 41 forward the sheet along a guide plate 42 into the nip of a pair of advancing rolls 43 which deposit the sheet within a collecting tray 16. The collecting tray 16 includes a base plate 44 inclined upwards and an upwardly turned margin stop 45.

The advancing rolls 43 serve to drive the sheet 2 into the collecting tray 16. The advancing rolls 43 further include a compact propelling mechanism 46 which moves the sheet 2 rapidly and efficiently into alignment against the stop 45. The propelling mechanism is described in greater detail in US. application, Ser. No. 317,028 filed Dec. 20, 1972.

Having thus described the operation of the fusing apparatus 1, further reference will now be given to the curl control means 6 in accordance with this invention.

In the embodiment of FIG. 3 the transport comprises a vacuum transport having a suction means 21 which draws air in through or between the belts 22. The suction means is connected to any conventional source of suction (not shown). The suction means 21 cooperates with the belts 22 to firmly hold a sheet 2 of final support material in contact with the transport. The suction means 21 comprises, however, only one of many possible external influences in the machine 10 which can cause an air flow through the fusing zone 5. The suction means 21 draws air in from an external port (not shown). Air flows through various passageways defined by the machine components and sub-stations. The paper path provides one of the key flow channels for the air which flows to the suction means 21. In the absence of the curl preventing means 6 in accordance with this invention air is drawn through the fuser 3 in order to satisfy the requirements of the suction means 21 as shown by the arrows 50. While this flow of air has a beneficial effect with respect to cooling the sheet 2 prior to its being received by the snuffing rolls 40 and 41, it has a deleterious effect in that it results in a substantial curl being formed in the sheet during fusing.

There is also in the fuser 3 shown an internal means which causes a flow of air through the fusing zone 5. The internal means comprises a series of orifices 38 in the platen 30 which communicate with a suction means comprising the chamber 37. The purpose of these orifices 38 is to provide a vacuum holddown for holding the sheet 2 in contact with the platen 30 as it passes through the fuser 3. When the sheet does not cover these orifices a substantial air flow is produced. The direction of this air flow will vary depending on whether the sheet is entering or leaving the fuser. Another internal cause of air flow comprises the conductive air currents associated with the fuser 3.

Therefore, as shown, an air flow through the fusing zone is created both by external influences and by in ternal influences. It is believed. however, that either of these influences alone would be sufficient to provide an air flow through the fusing zone which would result in a substantially curled copy sheet.

In accordance with this invention it is desired to reduce the flow of air through the fuser so to reduce the curl producing effects of the moisture gradients induced in the sheet 2 during fusing. The mechanism by which this is accomplished is not fully understood, but it is believed to be the result of a localized condition in the fusing zone which reduces the rate that the moisture is driven out of the sheet during the period the thermal and moisture gradients are caused in the sheet by fusing. This may, for example, be do to a localized increased vapor pressure condition which can form do to the restricted air flow and which temporarily prevents or reduces the rate at which moisture can exit from the sheet 2 until the thermal and moisture gradients in the sheet have been reduced or eliminated.

The temperature and moisture gradients in the portion of the sheet 2 being heated occur for an extremely short period of time, a matter of fractions of a second. Therefore, if the sheet can be sufficiently restrained during this period or if the rate of moisture evaporation from the sheet during the period can be reduced, curl 7 can be reduced.

In the specific apparatus 1 shown, without the curl preventing means 6 the sheets are subject to substantial trail edge curl 7 as shown in FIG. 2. Lead edge 9 curl is not pronounced because of the inner-action of the vacuum transport 20 prevents the sheet 2 from being deformed by the influence of the moisture gradients by restraining deformation of the sheet. However, after the sheet 2 leaves the vacuum transport 20 the trail edge 8 of the sheet is not sufficiently restrained and, therefore, is subject to substantial curl 7, as for exam ple, that shown in FIG. 2.

When the lead edge 9 of the sheet 2 enters the fusing zone 5 the remainder ofthe sheet closes off some of the suction ports (not shown) in the top of the vacuum transport 20 thus reducing the flow of air flow through the fusing zone 5. As the sheet 2 progresses through the zone 5, more of the suction ports, particularly those adjacent to the fuser 3, are uncovered by the sheet 2 thereby increasing the air flow through the zone. This is also believed to be a major factor in causing the pronounced trail edge 8 curl and insignificant lead edge 9 curl using the specific apparatus 1 shown.

Therefore, in accordance with this invention curl preventing means 6 are provided which comprise in the embodiment shown one or more seals 61, 62, 63 and 64 adjacent to the fusing zone 5 which are adapted to limit the air flow at the zone to an amount at which curl of the sheet is substantially reduced or eliminated. In the apparatus 1 shown which includes the external influence of the vacuum transport 20, the provision of the seal 61 between the top portion 65 of the fuser 3 and the upper transport roll 40 at the exit side of the fuser provides a substantial reduction in curl as compared to the same apparatus without the seal 61. Experimentally, the reduction in curl due to this seal 61 has been shown to be as much as about percent or more. Further reductions in curl can be achieved by providing additional seals 62, 63 and 64 as, for example, the lower seal 62 between the bottom portion 66 of the fuser 3 and the lower transport roll 41 has been determined to provide a further 5 percent to 10 percent or more improvement in curl reduction. At the upstream side of the fuser 3, because of the external influence of the vacuum transport 20, it has been found desirable to provide slots or holes 67 in the seal 63 between the fuser and the cleaning station E. This allows air flow from the channel 68 as shown by arrow 69 to flow to the transport and thereby reduces the amount of flow drawn through the fuser. The provision of holes 67 in this particular seal 63 which also serves to guide the sheet provides a further 15 percent or more improvement in curl 7 reduction. Finally, a seal 64 between the vacuum transport 20 and the lower portion 66 of the fuser 3 provides some improvement, but not that significant, namely, less than 5 percent.

It is quite apparent that the fusing apparatus illustrated in FIG. 3 requires seals between the downstream sheet transport 40 and 41 and the fusing apparatus 3 in order to substantially reduce or eliminate curl 7. It should also be apparent that had the vacuum transport 20 or other external source of substantial air flow through the fuser 3 been downstream of the fuser rather than upstream thereof, then the effective seals for reducing air flow through the fuser would have been the upstream seals 63 and 64, rather than the downstream seals 61 and 62. In this case the seal 63 between the upper portion 65 of the fuser 3 and the adjacent housing E would have had to be impervious, whereas the seals 61 and 62 on the downstream side of the fuser could have been pervious as desired.

In the embodiment shown the internal suction means 37 and 38 does not exert a controlling influence on the amount of curl which is formed. Regulation of the suction force here, in cooperation with the seals 61 64 could help reduce air flow through the fusing zone 5. Conversely increasing the suction force would restrain deformation caused by the moisture gradient, however, it would also increase the retardation forces on the sheet 2 which could cause the sheet to stall in the fuser 3 which is undesirable.

The location of the seals 61 64 has to be determined based on the air flow conditions in the apparatus in which the fuser 3 is employed and seals 61 64 may be employed at one or all of the locations shown in order to provide the reduced air flow through the fuser. The most significant seals will be those adjacent the image containing side of the sheet 2, for an apparatus where the sheet is passed over a platen 30, since it is on this side of the sheet that the greatest air flow occurs.

The seals 61, 62 and 63 shown comprise elongated strip-type members formed of a resilient material which is biased against the transports 20 or 40 and 41, and extend over the gaps between the transports or other housings (E) and the fuser. The seals 61 64 are at least coextensive with the fusing zone 5 in the transverse direction, (e.g., the direction normal to the plane of FIG. 3). The seals may be secured to the fuser by any desired means as, for example, adhesively. Preferably, the resilient material comprises a polymeric material such as polytetrafloroethylene sold under the trademark Tetlon, or polyethyleneterephthalate sold under the trademark Mylar which have been found to be us able materials as seals in accordance with this invention. Holes 67 or other perforations can be employed as in seal 63 to provide means for adjusting the degree to which the seal reduces the air flow through the fusing zone 5 as by providing an alternate air channel as shown. Preferably the seals should be heat resistant.

By way of example for a fuser 3 having a gap between the platen 30 and the reflector 32 of about /8 inch and a length normal to the plane of FIG. 3 of about inches an air flow of less than about .2 cfm will substan tially reduce or eliminate curl. If the seals 61 63 are removed the air flow through the fuser 3 shown would be about 5 cfm.

It is believed that for most radiant fusers the air flow should be maintained below about l cfm and preferably below about .2 cfm in order to reduce or eliminate curl.

It should be apparent from the foregoing description that the seals 61 63 of this invention do not necessarily completely prevent air flow from the respective air flow channels in which they are interposed though it would be preferable if they did. They do, however, at least baffle the air flow from the channel and thereby substantially reduce it. In FIG. 3, for example, the roll 40 has a plurality of spaced apart circumferential ridges 47 which allow a small air flow between the seal 61 and the roll 40, however, since the ridges 47 are not very high, generally less than .030 inch, the air flow is slight.

The toner images of this invention may be formed ,from toner of the types described in U.S. Pat. Nos.

2,807,703 and 2,807,704.

The patents, applications and texts referred to specif' ically in this application are intended to be incorpo' rated by reference into the application.

It is apparent that there has been provided in accordance with this invention, a fusing apparatus which fully satisfies the objects, means and advantages set forth hereinbefore. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.

What is claimed is:

1. In a fusing apparatus for heat fusing a toner image to a sheet of final support material including:

a fuser having a source of heat radiation for applica' tion to said sheet, said fuser defining a fusing zone wherein said heat source is effective to fuse said image to said sheet, and a flow of air at said Zone; the improvement wherein said apparatus further includes;

first transport means for transporting said sheet, said transport means being located adjacent said fuser, an air channel being defined between said transport means and said fuser; and

means cooperating with said fuser for reducing curl of said sheet during fusing, said curl reducing means comprising at least one seal extending over a gap between said fuser and said transport means for limiting air flow at said zone to an amount at which curl of said sheet is substantially reduced.

2. An apparatus as in claim 1 wherein said seal comprises an elongated strip-like member.

3. An apparatus as in claim 2 wherein said seal is biased against said transport means.

4. An apparatus as in claim 2 wherein said striplike member is formed of a resilient polymeric material.

5. An apparatus as in claim 1 wherein said first transport means is located at a first side of said fuser and wherein a second transport means is provided at the opposing side of said fuser and wherein at least one of said first and second transport means includes suction means cooperating therewith to hold said sheet to said one of said transport means.

6. An apparatus as in claim 1 including a plurality of said seals.

7. An apparatus as in claim 5 wherein a plurality of air channels are formed between the respective transport means and the fuser and wherein seals are interposed in the channels exteding over respective gaps between the fuser and the respective transport means.

8. An apparatus as in claim 7 wherein said first transport means comprises a pair of pinch rolls and wherein said second transport means comprises a vacuum transport having said suction means and wherein said first transport is located downstream of said fuser and wherein said second transport is located upstream of said fuser.

9. An apparatus as in claim 1 wherein said air flow is reduced to below 1 cubic foot per minute.

10. An apparatus as in claim 9 wherein said air flow is reduced to below 0.2 cubic foot per minute. 

1. In a fusing apparatus for heat fusing a toner image to a sheet of final support material including: a fuser having a source of heat radiation for application to said sheet, said fuser defining a fusing zone wherein said heat source is effective to fuse said image to said sheet, and a flow of air at said zone; the improvement wherein said apparatus further includes; first transport means for transporting said sheet, said transport means being located adjacent said fuser, an air channel being defined between said transport means and said fuser; and means cooperating with said fuser for reducing curl of said sheet during fusing, said curl reducing means comprising at least one seal extending over a gap between said fuser and said transport means for limiting air flow at said zone to an amount at which curl of said sheet is substantially reduced.
 2. An apparatus as in claim 1 wherein said seal comprises an elongated strip-like member.
 3. An apparatus as in claim 2 wherein said seal is biased against said transport means.
 4. An apparatus as in claim 2 wherein said strip-like member is formed of a resilient polymeric material.
 5. An apparatus as in claim 1 wherein said first transport means is located at a first side of said fuser and wherein a second transport means is provided at the opposing side of said fuser and wherein at least one of said first and second transport means includes suction means cooperating therewith to hold said sheet to said one of said transport means.
 6. An apparatus as in claim 1 including a plurality of said seals.
 7. An apparatus as in claim 5 wherein a plurality of air channels are formed between the respective transport means and the fuser and wherein seals are interposed in the channels exteding over respective gaps between the fuser and the respective transport means.
 8. An apparatus as in claim 7 wherein said first transport means comprises a pair of pinch rolls and wherein said second transport means comprises a vacuum transport having said suction means and wherein said first transport is located downstream of said fuser and wherein said second transport is located upstream of said fuser.
 9. An apparatus as in claim 1 wherein said air flow is reduced to below 1 cubic foot per minute.
 10. An apparatus as in claim 9 wherein said air flow is reduced to below 0.2 cubic foot per minute. 